The present invention is directed generally toward coal preparation plants and, more particularly, toward a new common correct media sump and wing tank apparatus for processing raw coal particles with a slurry of media and water.
Coal preparation plants separate organic and non-organic solid particles by their specific gravities. The coal preparation plant receives a feed of raw mined coal, and separates the raw mined coal into clean coal and refuse. Coal preparation plants typically utilize two basic processing methods for separating raw coal from rock and varying proportions of striated rock and coal from the higher quality coal. These two processing methods include heavy media and water based separation methods. Heavy media separation, utilizing a slurry of media, e.g., magnetite or ferrosilicon and water, to separate the coal from the refuse according to their specific gravity of dry solids, is the most common separation process for larger size (Plus 1 mm-0.5 mm) particles. Whereas, water based separation processes are more commonly used for the xe2x80x9ccleaningxe2x80x9d of the finer sized particles, as that term is commonly understood in the coal processing art.
Coal preparation plants may incorporate one or two heavy medium circuits for processing coal with a bottom size ranging from 0.5 mm to 2.0 mm. Often two separate processing methods, or circuits, are employed, namely, heavy media vessel and heavy media cyclone circuits for cleaning the coarser and finer coal size fractions, respectively.
Plants using heavy media processing require a pre-sized (removal of undersized and/or oversized particles) circuit feed. Raw coal screens are generally used to pre-size the correct media feed, whereas deslime screens are used to pre-size the heavy media cyclone feed, although a single screen may be used to pre-size the feed for both unit operations.
The raw coal screen receives the raw coal feed particles and separates them into coarse and undersized raw coal. The coarse or larger sized particles discharged from the raw coal screen surface are directed by gravity to the heavy media vessel. The deslime screen receives the undersized raw coal from the raw coal screen and separates it into intermediate and finer sized fractions. The raw coal particles discharged from the screen surface of the deslime screen are directed to the heavy media cyclone feed circuit, while the finer sized particles passing through the deslime screen are fed to the fine coal section of the coal preparation plant.
Traditionally, each heavy media feed circuit retains its own medium for recirculation, and thus requires separate medium storage sumps. These separate storage sumps increase the overall size of the plant area requirements, and add to the cost of building the coal preparation plant.
The present invention is directed toward overcoming one or more of the above-mentioned problems.
In a coal preparation plant which receives a raw coal feed and separates the raw coal into clean coal and refuse, an apparatus is provided for use therein. The inventive apparatus is a combined sump common to the heavy media vessel and heavy media cyclone circuits used for storage of the recirculating medium for the heavy media vessel circuit and a mixing device, referred to as a wing tank, to proportionally combine intermediate sized raw coal feed particles with a slurry of media and water for feeding the heavy media cyclone circuit. The advantage of this combined system is the ability to use a common recirculating media for use in both the heavy media vessel and heavy media cyclone circuits, without sacrificing the ability to have different recirculating gravities for each separating circuit.
The commonality between the two chambers of the combined apparatus is connecting the overflow of the wing tank to the correct media feed sump. The inventive apparatus includes a wing tank with an inlet receiving the intermediate sized raw coal directly from a deslime screen and a slurry of media and water from the drain portion of an underpan of at least one media recovery screen (refuse screen and clean coal screen) and an outlet by which the mixture of intermediate sized raw coal and slurry exits the column. The wing tank mixes the intermediate sized raw coal and the slurry of media and water according to a select proportion, and it is then pumped to a heavy media cyclone separation circuit, or section, of the coal preparation plant.
The inventive apparatus also includes a storage and feeding device, i.e, correct media sump, for retaining and distributing, via a pump, the recirculating medium used for the correct media circuit. The correct media feed sump includes a open top inlet for collection of the slurry of media and water from the drain portion of an underpan of at least one media recovery screen (refuse screen and clean coal screen) and an outlet by which the medium exits the sump.
In one form of the inventive apparatus, the wing tank is located adjacent to, or integrally formed with, the correct media feed sump, such that an overflow from the wing tank discharges into the correct media feed sump. The overflow is created when wetted intermediate raw coal particles discharged from the deslime screen are fed into the wing tank displacing an equivalent volume of media contained within the wing tank.
First and second nuclear density gauges may be provided for measuring the specific gravities of both the mixture output by the wing tank and the medium output by the correct media feed sump. The signals generated by the nuclear density gauges are received by control circuitry that adjusts the addition of water to the outputs of both chambers. Specifically, a water source is connected to the outputs of the wing tank and correct media feed sump via at least two control valves. The control circuitry adjusts the control valves to add water from the water source to the output mixtures based upon the measured specific gravity value of each mixture contained within the respective discharge pipes.
In another form, the inventive apparatus includes first and second pumps for discharging the mixture of raw coal and medium from the wing tank and medium only from the correct media feed sump. Each of the pumps has a suction connected to the respective storage device and an output connected to an input of the respective heavy media separating device, namely, vessel and cyclone separating devices. The water source is preferably connected between the respective storage device and each of the pump suctions, while the nuclear density gauges are preferably provided between the pump output and the respective heavy media separating device input.
In a further form, the inventive apparatus may include an over dense media splitter box, at least one bleed box, and a common medium distribution box. Over dense media from a magnetic separator, which is used to recover magnetite from the effluent streams from both of the heavy media separating circuits, is collected and distributed to the two chambers of the common correct sump/wing tank via the over dense media splitter box. The over dense media splitter box preferably contains a pneumatically controlled actuator driven by a signal generated from the plant control circuitry.
The common medium distribution box receives the slurry of media and water from the drain portion of the underpan of at least one media recovery screen. The bleed box is used to remove extraneous amounts of non-magnetics and water from the recirculating medium in the common medium distribution box. A quantity of the recirculating medium is bled from the system proportional to the feed contaminants. The bleed box device preferably contains a pneumatically controlled actuator driven by a signal generated from the plant control circuitry.
In an alternate form, the common medium distribution box may be removed and the return media proportionally fed directly to the wing tank and the common correct media sump. In this alternate form, the bleed box can be fed by any other means containing correct or return media as will be appreciated by one of ordinary skill in the art.
A method of combining the medium requirements for two separate media separating devices is also provided. The method generally includes the steps of receiving, at a combined wing tank/correct media feed sump, a slurry of media and water from the drain portion of an underpan of at least one media recovery screen (refuse screen and clean coal screen), receiving sized raw coal directly from a deslime screen, and mixing the raw coal and slurry in the wing tank according to a select proportion having a select specific gravity, such that overflow from the wing tank is received directly by the common correct media sump.
In one form, the inventive method further includes the steps of measuring the specific gravities of the outputs of both the wing tank, containing the sized raw coal and slurry mixture, and the correct media feed sump, containing a medium of water and magnetite. Additional water is individually added to the output flows of each storage unit in response to the measured specific gravities of each stream to maintain the selected specific gravity in each respective stream. Two pumps may be provided, one for feeding the sized raw coal and slurry mixture from the wing tank to a heavy media cyclone separating device, and one for feeding the media from the correct media feed sump to the heavy media vessel separating device. The pumps are generally provided between the storage chamber outputs and the input of the respective heavy media separating device.
Two nuclear density gauges may be provided for measuring the specific gravities of each respective flow stream. In a preferred form, the specific gravity of each stream is measured downstream of the respective pump and upstream of the respective heavy media separating device. Water is preferably added to each stream flow, in response to the measured specfic gravity value, downstream of the respective medium storage device and upstream of the respective discharge pump.
In another form of the inventive method, the wing tank is located adjacent to, or integrally formed with, the correct media feed sump, such that the overflow from the wing tank discharges directly into the correct media feed sump.
It is an object of the present invention to:
remove the need for a separate heavy media cyclone feed sump in coal preparation plants;
provide the ability to use a common recirculating media for use in both the heavy media vessel and heavy media cyclone circuits, without sacrificing the ability to have different recirculating gravities in each separating device circuit; and
provide a common apparatus for storage of the recirculating media and for mixing the raw coal particles and the slurry of media and water, while occupying minimal space in a coal preparation plant.
Other objects, aspects and advantageous of present invention can be obtained from a study of the specification, the drawings, and the appended claims.